This invention relates to producing a viscous heavy oil and treating it in a field location by diluting the oil with conversion products of its asphaltenes to provide a pumpable liquid oil product.
Numerous prior processes for treating viscous heavy oils have been described in patents and publications such as the following:
In 1941 an article by M. W. Ball, "Development of the Athabasca Oil Sands," Canadian Institute of Mining and Metallurgy Transactions, Volume XLIV, pages 59-91, indicated that the crude oil obtained from Athabasca tar sands is uniquely susceptible to digestion at mild temperatures and relatively long times; which can provide a change in API gravity such as from as low as about 10 to more than 20.
In 1964, an article by J. G. Erdman and J. P. Dickie, "Mild Thermal Alteration of Asphaltic Crude Oils", Symposium on Asphalt: Composition, Chemistry and Physics, presented before the Division of Petroleum Chemistry, American Chemical Society, Philadelphia Meeting, April 5-10, stated, "That asphaltic crude oils and particularly asphaltic petroleum bottoms are liable to heat is well known, the process of `visbreaking` having been practiced in petroleum refinery for many years" (page B-69). The authors indicated that, "If the results obtained on the fractions of crude oil are paralleled, at least approximately in the whole crude or in a vacuum residium, a more stable residual fuel oil might be obtained by deasphalting visbreaking the remainder, followed by reconstitution" (page B-77).
In 1978 an article in Fuel, Volume 57, July 1978, by G. E. Moschopedis, S. Parkash and J. G. Speight, "Thermal Decomposition of Asphaltenes," indicated that the thermal decomposition of Athabasca asphaltenes occurred readily at a variety of temperatures to yield products varying from low-molecular-weight gases to presumably high-molecular-weight materials that are insoluble in benzene. In 1983, writing for the Distinguished Author Series, M. A. Carrigy on "Thermal Recovery From Tar Sands, " December 1983, JPT pp. 2149, states that "Probably the most significant lesson that has been learned from the many field tests in tar sands is that unpredictable variability in the reservoir is the most important factor initiating against the success of field experiments."
In 1980, SPE Paper 9510 by M. H. Waxman, C. T. Deeds and P. J. Closmann described laboratory work for obtaining mobility data regarding tar from Peace River Bullhead Sand in its parent core material at conditions simulating those involved in a steam drive oil recovery process. Asphaltene components of the tar were separated and heated at 572.degree. F. for 240 hours. That work indicated that, "The soluble asphaltenes became less stable in their maltene solutions" (page 4) and it was concluded that, "The ability of these altered asphaltenes to interact with organic solvents and/or their maltenes is reduced" (page 8). In addition, it was found that when the maltenes remaining after the removal of the asphaltenes were heated for times and temperatures such as 572.degree. F. for 240 hours or 617.degree. F. for 406 hours these treatments produced asphaltenes in the amounts of, respectively, 0.64 and 18.78% by weight.
Several United States patents relates to utilizing thermal alteration of heavy crude oils or their components. U.S. Pat. No. 3,442,333 describes upgrading heavy crude oil as it is being produced in the field by heating it in tubing strings and/or casings, at from about 550.degree. to 700.degree. F. for at least 24 hours. U.S. Pat. No. 3,554,285 describes upgrading crude oil by heating a reservoir to at least 550.degree. F. and inflowing crude oil and keeping it within the heated reservoir long enough to effect an upgrading of the oil.
Various patents such as U.S. Pat. Nos. 4,169,782; 4,294,686; 4,390,410 and 4,284,139 describe various ways of improving the refining of heavy crude oils by utilizing relatively mild visbreaking treatments in conjunction with other conventional refining treatments.